Chapter 27, Problem 7A

Summary Introduction

Introduction: Echinoderms are deuterostomes which represent a significant transition in animal phylogeny. Echinoderms are aquatic mammals and are the only species to have a deuterosome development and an endoskeleton in evolutionary history.

Answer to Problem 7A

Correct answer:

The correct answer is option (A) endoskeleton, pedicellariae, spines

Explanation of Solution

Explanation/justification for the correct answer:

Option (A) endoskeleton, pedicellariae, spines. The endoskeleton, which is considered a test and is composed of strong calcium carbonate plates, covers the sea urchins internal organs. There are pedicellariae on the skin of echinoderms, small pincers which help to capture food and remove foreign materials from the skin. Spines defend the urchin at sea and help in movement. So, the correct answer is option (A).

Explanation for incorrect answer:

Option (B) madreporite, tentacles, endoskeleton. Water flows through the madreporite into the body, and then through the ring canal in which it is dispersed to the bottom of the drain. Echinoderm bears no tentacles. So, this is an incorrect answer.

Option(C) water-vascular system, ampulla, pedicellariae. Echinoderms have a water-vascular system that is a fluid-filled, near tube system that works together to allow echinoderms to transfer and get food. The other end of the tube foot is a muscle fibre, called the ampulla. So, this is an incorrect answer.

Option (D) exoskeleton, pedicellariae, spines. The endoskeleton, which is considered a test and is constructed from rough calcium carbonate plates, covers the sea urchin's internal organs. So, this is an incorrect answer.